A party producing a witness shall not be allowed to impeach his credit by general evidence of bad character, but he may, in case the witness shall in the opinion of the court prove adverse, by leave of the court, prove that he has made at other times a statement inconsistent with his present testimony; but before such last mentioned proof can be given the circumstances of the supposed statement, sufficient to designate the particular occasion, must be mentioned to the witness, and he must be asked whether or not he has made such statement. In every such case the court, if requested by either party, shall instruct the jury not to consider the evidence of such inconsistent statements, except for the purpose of contradicting the witness.